LED Panel

[sherman]

The horizontal axis is the wavelength, in nanometers, and vertical axis is adsorption, in arbitrary units. You can see from the graph that violet and blue colors strongly prevail over red (note that for red spectrum, the 660-680nm range is preferable).
Our main conclusion from the above is that violet and blue light are most important for marine photosynthetic organisms.

[sherman]

Three main factors which affect the coloration of the coral most: light spectrum and intensity, the amount of food available in water (although coral polyps receive a significant portion of their energy from the zooxanthellae, they are also able to capture food particles from the water column), and from the purity of the water. 

This last factor is easiest to control.
The second factor, too, can be solved easily since there are a number of quality coral foods readily available on the market. At the same time many aquarists believe that, if there are fish living in a reef aquarium, corals will get sufficient food from small particles which float around from feeding the fish (and fish poo too is consumed by corals).Light is the last important factor required for good health and the coloration of corals

[sherman]

Corals can be very variable, and even the same species may contain different chromoproteins (proteins responsible for coloration)
Many of these proteins are fluorescent; i.e., they adsorb the light of a certain wavelength and radiate a different wavelength

[sherman]

Fig. 5 shows four specimens of the same species, Acropora millepora, in which different chromoproteins prevail:

 

[sherman]

(A) low concentration of chromoproteins, the color of zooxanthellae dominates; (B) green fluorescent proteins; (C) red fluorescent proteins; (D) non-fluorescent chromoproteins.

[sherman]

The strongest fluorescence will be observed in 400-450nm range, particularly because the eye sensitivity in that range is very low. The light in this range is usually called "actinic light.

The light in the 400-500nm range also has other importance: it is the most optimal light to promote marine photosynthesis. Therefore this part of the spectrum is of utmost importance for a reef tank

 

[sherman]

The conclusion of the article is that "the enhancement of coral pigmentation is primarily dependent on the blue component of the spectrum and regulated at the transcriptional level

[sherman]

The intensity of light is also very important for growth and active production of fluorescent chromoproteins.

The saturation limit of photosynthesis is about 600-700μmol·photons/m2/s.

However, it is not always a good idea to provide as much light in home aquaria, since a coral can become very demanding to its environment parameters under such high levels of illumination. Under less than perfect conditions such high levels of illumination can yield a contrary result: coral bleaching.

Concluding from the above, light in the 400-500nm range is most beneficial for marine photosynthetic organisms, and its shortwave portion (400-450nm) is most useful for their bright coloration.

[sherman]

The advantage of using LED are:

Advantage #1: Higher efficiency and less heat generation
Higher efficiency has two components. First is that LEDs are about twice more efficient than conventional fluorescent tubes or Metal Halide bulbs in converting the electric energy into light. Second is that LEDs only radiate in one direction of the plane and hence are not apt to block their own light.

[sherman]

Advantage #2: Extended life cycle

As a solid-state light source, a light emitting diode does not have quickly wearing parts, such as an incandescent filament. When operated at or below rated current, and providing that they do not overheat, high quality LEDs degrade very slowly.

[sherman]

Lifespan of the best LEDs available in the market today (Cree XT-E, LUXEON Rebel ES) is indeed very high, if sufficient heat removal and properly conditioned power are provided.
If all the required operation conditions are fulfilled, we will still be getting about 70% of LED's initial radiation power after 40 (150) thousand hours of operation. These figures translate to 10 (33) years of operation of a light fixture, providing 12 hours of operation daily! After this period the LEDs will continue to lose luminance, reaching about 50% of the initial value after 100 (200) thousand hours!

[sherman]

In comparison, conventional fluorescent tubes need to be replaced once every four to six months.
it means that they will have to be replaced at least 20 times during the lifetime of a LED fixture

[sherman]

Advantage #3: Ability to adjust illumination and spectrum
When using dimmable drivers, the light emitted by LEDs can be easily adjusted.

[sherman]

Natural illumination 

Natural illumination under water is not sufficient for photosynthesis until the sun rises approximately 15 degrees over the horizon. In approximately 30 minutes after this the illumination quickly increases to about half of the daily maximum value. Therefore actual photoperiod is about 9 hours.

[sherman]

That is all the day.

[monkeysee]

Nice information. Any photos of your latest light build ?

Sent from Singapore Reef Club mobile app

[sherman]

Waiting for parts to be in

 

[sherman]

Today let us consider important characteristics of light
First such characteristic is CCT - Correlated Color Temperature. CCT of a given light source characterizes the temperature of an absolutely black body that would radiate a similar spectrum. The hotter the black body, the higher will be the CCT and the more blue or "cold" will be the light. As an illustration, sunlight has a yellow tint, whereas blue giants - huge stars with high temperature of the surface: 10000K and above (Sirius, for example) - seem bluish even to the naked eye

[sherman]

Another important characteristic is CRI - the Color Rendition Index. 
To determine the CRI, a set of 8 standard color samples is illuminated with the source and with the light of a back body with the same color temperature. If none of the samples change their color, CRI is equal to 100.

[sherman]

It is important to know, however, that CRI is calculated for light sources with a particular color temperature. It is not appropriate to compare a 2700K, 82 CRI light source with a 5000K, 85 CRI source.
Also note that CCT and CRI are only defined for full-spectrum light sources. The CRI of monochromatic light is close to zero, and its CCT cannot be calculated.
All fluorescent and MH bulbs have a discrete spectrum, whereas sunlight has a continuous spectrum. Discrete spectrum is a result of using a discharge in mercury (and other metal) vapors, with several peaks at different wavelengths, mostly in the ultraviolet range. Phosphors on the bulb convert this radiation into narrow bands of visible light. A discrete spectrum vs. continuous is shown in Fig. 18:

[sherman]

Fig.18

[sherman]

The gaps - wavelengths that are missing in a discrete spectrum - mean that certain tints of color cannot be correctly rendered under such illumination and, as a result, the light source will have a low color rendition index (CRI).

Meaning that when using these bulbs precise color rendition cannot be achieved.
we can safely state that maximum radiation in the required range is only achieved when a CCT of approximately 20000K is declared.

High CCT bulbs are often characterized by a significant portion of radiation in the 420-430nm range. Experienced reef aquarists recommend 20000K bulbs for providing the best color for marine organisms. This advice, obtained through years of practice, matches well with the conclusions we derived above.

[sherman]

Let us now consider the spectrum radiated by various LEDs. The spectrum of a cool-white LED with CCT around 7000K is shown in Fig. 21.

 

Fig.21

 

 

[sherman]

Radiation of the Blue LED is most suitable to compensate for the required 470-490nm range. Even a better match could be achieved by using a LED with a 475nm peak - fortunately, such LEDs exist!

To better explain this, let us consider the term bin, which manufacturers use to characterize their LEDs. A bin is a group of LEDs that have been selected according to a certain parameter. There are efficiency bins, CCT and CRI bins, and dominating wavelength (DWL) bins are available for monochromatic (single color) LEDs. DWL bins for blue LUXEON Rebel color LEDs are shown in Table 1.

[sherman]

Table 1